Green mining method for bauxite under coal

Abstract

The present invention relates to the technical field of bauxite mining, and particularly relates to a green mining method for bauxite under coal, mainly solving the technical problems existing in the current mining of bauxite under coal, such as pollutants in the goaf of the upper coal seam being easily introduced into the aluminum layer, low recovery rate, easy caving of the overlying strata, and generation of a large amount of solid waste polluting the environment. This method includes: S1. Selecting the target rock stratum; S2. Conducting permeability transformation on the target rock stratum; S3. In-situ pre-cracking of bauxite; S4. Pillarless fully mechanized bag filling mining. This method can prevent old kiln water and toxic and harmful gases in the goaf of the coal seam from entering the aluminum mining face during the mining of the aluminum layer, greatly improving the safety of the aluminum layer mining operation; it can weaken the strength of the ore body, reduce the loss of fully mechanized mining equipment, and improve the fully mechanized mining efficiency; it can also improve the recovery rate of bauxite and prevent the overlying strata from caving; it can also scale and greenly treat and utilize coal gangue and red mud, avoiding the impact of industrial solid waste such as coal gangue and red mud on the ecological environment.

Description

Technical Field

[0001] The present invention relates to the technical field of bauxite mining, and particularly to a green mining method for bauxite under coal seams. Background Art

[0002] The reserves of bauxite resources in China are extremely rich. Among them, the reserves of bauxite resources in Shanxi Province account for about 40% of the country's total, ranking first in the country. Most of the bauxite in Shanxi Province occurs in the Benxi Formation of the Middle Carboniferous System, is closely associated with the Permian coal seams, and underlies the coal-bearing strata.

[0003] The existing mining of bauxite under coal seams has the following technical problems:

[0004] Firstly, in the actual production process, considering factors such as investment and production efficiency, the general mining sequence of coal and bauxite resources is the downward mining method, that is, coal is mined first and then bauxite. During the downward mining process, a large amount of pollutants such as mine pit wastewater and toxic and harmful gases may accumulate in the goaf of the upper coal seam, and coal mining will cause the development of fissures in the floor rock strata. If the fissures in the roof rock strata are connected with the fissures in the coal seam floor rock strata during bauxite mining, it will lead to the entry of pollutants into the bauxite mining area, which will not only affect the safety and efficiency of mining operations, but also may pollute the underground environment.

[0005] Secondly, due to the relatively large hardness of bauxite ore, the cutting ability of general fully mechanized tunneling equipment cannot meet the normal mining requirements, and the equipment loss is serious. Therefore, at present, the bauxite mining mainly adopts the blasting method for caving mining, and a large number of ore pillars are reserved to support the roof after mining, resulting in a relatively low bauxite recovery rate of only about 50%. At the same time, under the long-term load action, the bearing capacity of the ore pillars will gradually weaken. If the ore pillars become unstable and cause the overlying strata to collapse, it may lead to the destruction of the upper water system, ground settlement, and ecological environment damage and geological disasters.

[0006] Thirdly, a large amount of industrial solid waste such as coal gangue and red mud is generated during the production and washing processes of coal mines and bauxite mines. If it cannot be effectively disposed of, it will seriously affect the ecological environment.

[0007] Based on this, it is urgent to explore a green mining method suitable for bauxite under coal seams. Summary of the Invention

[0008] To overcome the technical defects existing in the existing mining of bauxite under coal seams, such as the easy entry of pollutants in the goaf of the upper coal seam into the bauxite layer, low recovery rate, easy collapse of the overlying strata, and the generation of a large amount of solid waste polluting the environment, the present invention provides a green mining method for bauxite under coal seams.

[0009] The green mining method for bauxite under coal seams provided by the present invention includes the following steps:

[0010] S1. Select the target rock stratum:

[0011] Explore the rock layer distribution between the coal seam and the aluminum layer, and select the rock layer with a relatively large porosity as the target rock layer;

[0012] S2. Conduct permeability transformation on the target rock layer:

[0013] Adopt the multi-branch horizontal directional drilling and grouting technology to inject the coal gangue-based slurry into the target rock layer to improve the anti-seepage property of the target rock layer;

[0014] S3. In-situ pre-fracture of bauxite:

[0015] Adopt the horizontal directional drilling and grouting technology to inject the fracturing fluid into the aluminum layer to generate fractures in the bauxite in the aluminum layer;

[0016] S4. Pillarless fully mechanized bag filling mining:

[0017] Divide the aluminum layer into several ore blocks with a preset length along the mining direction; as the fully mechanized mining equipment advances forward, hang the filling bags on the roof of each mined ore block in turn, and pump the red mud-based slurry into the filling bags to support the ore block after solidification.

[0018] Optionally, the step S2 includes the following sub-steps:

[0019] S21. Expand 15m to 60m outward from the boundary of the lower aluminum mining face as the construction area of the target rock layer;

[0020] S22. Arrange the wellhead on the left side of the construction area, use a single-bend screw drill to vertically drill a first vertical main well reaching the target rock layer on the ground, and simultaneously carry out the operations of lowering the casing and cementing the casing;

[0021] S23. Continue to drill horizontally to the right to the first horizontal main well at the right boundary of the construction area, and simultaneously carry out the operations of lowering the casing and cementing the casing;

[0022] S24. Adopt the method of backward side drilling to drill horizontal branch wells on both sides of the first horizontal main well;

[0023] S25. Install oil pipes in the first vertical main well and the first horizontal main well, pump the coal gangue-based slurry to the horizontal branch wells through the oil pipes, and inject the coal gangue-based slurry into the target rock layer through the spraying pipes;

[0024] S26. Adopt the backward method to carry out the grouting operation of the next horizontal branch well until the construction of the entire construction area is completed.

[0025] Optionally, the horizontal branch wells on both sides of the first horizontal main well are distributed in a plume shape.

[0026] Optionally, the coal gangue-based slurry is a mixture of coal gangue fine aggregate, ultrafine cement, and water.

[0027] Optionally, step S3 includes the following sub-steps:

[0028] S31. Insert a single-bend positive displacement motor into the first vertical main shaft and drill vertically downward at the turning point of the first vertical main shaft to reach the second vertical main shaft of the aluminum layer, and simultaneously conduct casing running and pipe cementing operations;

[0029] S32. Continue to drill horizontally to the right to the second horizontal main shaft at the right boundary of the aluminum mining face, and simultaneously conduct casing running and pipe cementing operations;

[0030] S32. Install a fracturing pipe in the second vertical main shaft and the second horizontal main shaft, and install a fracturing device at the front end of the fracturing pipe;

[0031] S33. Pump the fracturing fluid into the fracturing device, and the fracturing device injects the fracturing fluid into the aluminum layer to generate fractures in the bauxite of the aluminum layer;

[0032] S34. Use a backward method to complete the fracturing of the bauxite in the entire aluminum mining face.

[0033] Optionally, the fracturing fluid is a mixture of water, sand, and additives.

[0034] Optionally, the red mud-based slurry is a mixture of red mud fine aggregate, cement, and water.

[0035] The technical solution provided by the present invention has the following advantages compared with the prior art:

[0036] 1) The green mining method for subcoal bauxite provided by the present invention uses the multi-branch horizontal directional drilling and grouting technology to carry out permeability transformation on the target rock layer with relatively large porosity between the coal seam and the aluminum layer, which can prevent the old kiln water and toxic and harmful gases in the goaf of the coal seam from entering the aluminum mining face during the mining of the aluminum layer, greatly improving the safety of the aluminum layer mining operation;

[0037] 2) The green mining method for subcoal bauxite provided by the present invention uses the ground large-scale ore body fracturing technology to pre-fracture the ore body before the aluminum layer mining operation, which can weaken the ore body strength, reduce the loss of fully-mechanized mining equipment, and improve the fully-mechanized mining efficiency;

[0038] 3) The green mining method for subcoal bauxite provided by the present invention uses the comprehensive mechanized mining combined with the bag filling method for the goaf to mine the ore body, which can greatly improve the recovery rate of bauxite and extend the service life of the mine; and can prevent the overlying rock strata from caving, effectively protecting the upper water system;

[0039] 4) The green mining method for bauxite under coal provided by the present invention uses a coal gangue-based slurry mainly composed of coal gangue waste to transform the permeability of the target rock formation, and uses a red mud-based slurry mainly composed of red mud waste to fill the mined-out area, which can scale and greenly treat and utilize coal gangue and red mud, avoid the impact of coal gangue and red mud industrial solid waste on the ecological environment, and achieve green, low-carbon and high-quality development of the mine. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The drawings herein are incorporated into the specification and form a part of this specification, showing embodiments consistent with the present invention and, together with the specification, are used to explain the principles of the present invention.

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention or in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0042] Figure 1 It represents a schematic structural diagram of the formation targeted in the embodiments of the present invention;

[0043] Figure 2 It represents a flow chart of the green mining method for bauxite under coal in the embodiments of the present invention;

[0044] Figure 3 It represents a schematic diagram of the working section of step S2 in the embodiments of the present invention;

[0045] Figure 4 It represents a schematic top view of the operation of step S2 in the embodiments of the present invention;

[0046] Figure 5 It represents a schematic installation structure diagram of the grouting pipe in the embodiments of the present invention;

[0047] Figure 6 It represents a schematic diagram of the working section of step S3 in the embodiments of the present invention;

[0048] Figure 7 It represents a schematic top view of the operation of step S3 in the embodiments of the present invention;

[0049] Figure 8 It represents a schematic installation structure diagram of the fracturing device in the embodiments of the present invention;

[0050] Figure 9 It represents a schematic diagram of the working section of step S4 in the embodiments of the present invention.

[0051] In the figure:

[0052] 100, Aquifer; 200, Coal seam; 300, Aluminum layer; 400, Mudstone layer; 500, Sandstone layer; 600, Coal pillar; 700, Goaf;

[0053] 1, Ore block; 2, Fully-mechanized mining equipment; 3, Filling bag; 4, Red mud-based slurry; 5, Aluminum mining face; 6, Construction area; 7, First vertical main shaft; 8, First horizontal main shaft; 9, Horizontal branch well; 10, Oil pipe; 11, Shotcreting pipe; 12, Second vertical main shaft; 13, Second horizontal main shaft; 14, Fracturing pipe; 15, Fracturer; 16, First packer; 17, Connecting rod; 18, Second packer. Detailed implementation manners

[0054] In order to be able to more clearly understand the above-mentioned objects, features and advantages of the present invention, the solution of the present invention will be further described below. It should be noted that, without conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0055] In the description, it should be noted that the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0056] Many specific details are set forth in the following description in order to fully understand the present invention, but the present invention can also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only a part of the embodiments of the present invention, rather than all the embodiments.

[0057] The following combines Figures 1 to 9 to detail the specific embodiments of the present invention.

[0058] Referring to Figure 1 , the strata of the second mining area of a bauxite deposit under coal in Shanxi Province are targeted in this embodiment. From top to bottom, there are Quaternary, Neogene, Permian and Carboniferous in sequence; the groundwater content in the Quaternary and Permian is rich, and each has an aquifer 100; there are a coal seam 200 and an aluminum layer 300 in the Carboniferous. The average buried depth of the coal seam 200 is 182 m and the average thickness is 4.6 m. The average buried depth of the aluminum layer 300 is 210 m and the average thickness is 3.8 m. The aluminum mining face 5 is about 500 m long and about 150 m wide. Between the coal seam 200 and the aluminum layer 300, there are mudstone layers 400, sandstone layers 500 and mudstone layers 400 distributed from top to bottom in sequence; the mudstone layer 400 has a muddy texture, mainly composed of clay minerals, and the porosity is about 9%; the sandstone layer 500 has a silt-like texture, mainly composed of quartz, and the porosity is about 25%. Restricted by the early mining technology level, a large number of coal pillars 600 are reserved in the residual mining area of the coal seam 200 to support the overlying strata; due to the ultra-high development of the water-conducting fissure zone affected by mining, a large amount of old kiln water and toxic and harmful gases have accumulated in the goaf 700 of the coal seam 200.

[0059] Reference Figures 2 to 9 , this embodiment provides a green mining method for bauxite under coal seams, including steps S1 to S4.

[0060] S1. Select the target rock stratum: Explore the rock stratum distribution between the coal seam 200 and the bauxite layer 300, and select the rock stratum with a relatively large porosity as the target rock stratum.

[0061] It should be noted that the so-called relatively large means: taking several rock strata between the coal seam 200 and the bauxite layer 300 as comparison objects, having the largest porosity. For example, in this embodiment, there are two mudstone layers 400 and one sandstone layer 500 between the coal seam 200 and the bauxite layer 300, and the porosity of the sandstone layer 500 is greater than that of the mudstone layer 400, so the sandstone layer 500 is selected as the target rock stratum.

[0062] S2. Conduct permeability transformation on the target rock stratum: Adopt the multi-branch horizontal directional drilling grouting technology to inject coal gangue-based slurry into the target rock stratum to improve the anti-seepage property of the target rock stratum.

[0063] Specifically, the coal gangue-based slurry in this embodiment is a mixture of coal gangue fine aggregate, ultra-fine cement and water, and the particle size of the coal gangue fine aggregate is 0 mm to 5 mm.

[0064] More specifically, the component mass ratio of the coal gangue-based slurry in this embodiment is: coal gangue fine aggregate: ultra-fine cement: water = 1:0.3:1.3. During specific implementation, the component mass ratio of the coal gangue-based slurry can be adjusted in a timely manner according to the grouting situation, so that the permeability coefficient of the target rock stratum after grouting is less than 0.01 m / d.

[0065] Specifically, step S2 of this embodiment includes the following sub-steps: S21. Expand 15 m to 60 m outward from the boundary of the lower bauxite mining face 5 as the construction area 6 of the target rock stratum; S22. Arrange the wellhead on the left side of the construction area 6, and use a single-bend screw drill to vertically drill a first vertical main well 7 reaching the target rock stratum on the ground, and simultaneously carry out the operations of installing the casing and cementing the pipe; S23. Continue to drill horizontally to the right to the first horizontal main well 8 at the right boundary of the construction area 6, and simultaneously carry out the operations of installing the casing and cementing the pipe; S24. Adopt the method of backward side drilling to drill horizontal branch wells 9 on both sides of the first horizontal main well 8; S25. Install oil pipes 10 in the first vertical main well 7 and the first horizontal main well 8, pump the coal gangue-based slurry into the horizontal branch wells 9 through the oil pipes 10, and inject the coal gangue-based slurry into the target rock stratum through the grouting pipe 11; S26. Adopt the backward method to carry out the grouting operation of the next horizontal branch well 9 until the construction of the entire construction area 6 is completed.

[0066] More specifically, when the grouting pipe 11 of this embodiment works in the horizontal branch well 9, first packers 16 are provided at both ends. Under the sealing action of the two first packers 16, the coal gangue-based slurry is injected into the sandstone layer 500 through the grouting pipe 11; after grouting a certain distance, the grouting pipe 11 is pushed forward by the connecting rod 17 for the next section of grouting until the grouting in the horizontal branch well 9 is completed. Specifically, under the pressure of the grouting pump, the spraying and diffusion range of the grouting pipe 11 of this embodiment in the sandstone layer 500 can reach up to 30 m at most.

[0067] It should be noted that the single-bend positive displacement motor is a mature device in the prior art, which can change the well inclination angle and azimuth angle to achieve precise control of the wellbore trajectory. For example, as shown in "Discussion on the Causes and Prevention Measures of Well Inclination Angle in Oil Drilling Construction" published by Yu Hui in the 23rd issue of China Petroleum and Chemical Standard & Quality in 2023, so the structure of the single-bend positive displacement motor will not be elaborated here.

[0068] More specifically, the horizontal branch wells 9 located on both sides of the first horizontal main well 8 in this embodiment are distributed in a feather shape, which can solve the problem of unstable wellbore caused by concentrated sidetracking at one sidetracking point. Specifically, the horizontal branch wells 9 on the same side are spaced 60 m apart, and the horizontal branch wells 9 on the opposite sides are spaced 30 m apart.

[0069] S3. In-situ pre-fracturing of bauxite: Using the horizontal directional drilling and grouting technology, fracturing fluid is injected into the aluminum layer 300 to cause fractures in the bauxite in the aluminum layer 300.

[0070] Specifically, the fracturing fluid is a mixture of water, sand and additives.

[0071] Specifically, step S3 of this embodiment includes the following sub-steps: S31. Use a single-bend positive displacement motor to extend into the first vertical main well 7 and vertically drill downward at the turning point of the first vertical main well 7 to form the second vertical main well 12 reaching the aluminum layer 300, and simultaneously carry out the operations of lowering the casing and cementing the pipe; S32. Continue to drill horizontally to the right to the second horizontal main well 13 at the right boundary of the aluminum mining face 5, and simultaneously carry out the operations of lowering the casing and cementing the pipe; S32. Install the fracturing pipe 14 in the second vertical main well 12 and the second horizontal main well 13, and install a fracturing device 15 at the front end of the fracturing pipe 14; S33. Pump the fracturing fluid into the fracturing device 15, and the fracturing device 15 injects the fracturing fluid into the aluminum layer 300 to cause fractures in the bauxite in the aluminum layer 300; S34. Use the retracting method to complete the fracturing of the bauxite in the entire aluminum mining face 5.

[0072] It should be noted that the second vertical main well 12 is formed by continuing to drill downward from the first vertical main well 7 to reach the aluminum layer 300, so the second vertical main well 12 includes the first vertical shaft.

[0073] More specifically, when the fracturing device 15 of this embodiment operates in the second horizontal main well 13, second packers 18 are provided at both ends. Under the sealing action of the two second packers 18, the fracturing fluid is injected into the aluminum layer 300 in the horizontal direction through the fracturing device 15. Specifically, under the pressurization of a high-pressure pump, the maximum diffusion range of the cracks formed after the aluminum layer 300 of this embodiment is fractured can reach 80 m.

[0074] S4. Pillarless fully mechanized bag filling mining: The aluminum layer 300 is divided into several ore blocks 1 of a preset length along the mining direction; as the fully mechanized mining equipment 2 advances forward, filling bags 3 are successively suspended on the roof of each mined ore block 1, and red mud-based slurry 4 is pumped into the filling bags 3 to support the ore block 1 after solidification.

[0075] It is easy to understand that the preset length of the ore block 1 should be less than the periodic weighting interval of the basic roof to prevent the roof from caving during the mining process.

[0076] It should be noted that before pumping the red mud-based slurry 4 into the filling bag 3, air can be first injected into the filling bag 3 to make it expand.

[0077] Specifically, the red mud-based slurry 4 of this embodiment is a mixture of red mud fine aggregate, cement, and water, and the particle size of the red mud-based fine aggregate is 0 mm to 5 mm.

[0078] More specifically, the mass ratio of the components of the red mud-based slurry 4 of this embodiment is: red mud fine aggregate:cement:water = 1:0.2:0.7, and the compressive strength of the filling body after the red mud-based slurry 4 solidifies can reach 20 MPa.

[0079] The above are only specific implementation manners of the present invention, enabling those skilled in the art to understand or implement the present invention. Although the above embodiments have been described in detail, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the above embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the above embodiments, and they should all be covered by the protection scope of the claims.

Claims

1. A green mining method for bauxite under coal, characterized in that, It includes the following steps: S1. Select the target rock stratum: Explore the rock stratum distribution between the coal seam (200) and the aluminum layer (300), and select the rock stratum with a relatively large porosity as the target rock stratum; there is accumulated old goaf water and toxic and harmful gases in the coal seam (200). S2. Conduct permeability transformation on the target rock stratum: Adopt the multi-branch horizontal directional drilling grouting technology to inject the coal gangue-based slurry into the target rock stratum to improve the anti-seepage performance of the target rock stratum; the coal gangue-based slurry is a mixture of coal gangue fine aggregate, ultrafine cement and water; the component mass ratio of the coal gangue-based slurry is coal gangue fine aggregate: ultrafine cement: water = 1:0.3:1.3, so that the permeability coefficient of the target rock stratum is less than 0.01 m / d. The step S2 includes the following sub-steps: S21. Expand 15 m to 60 m outward from the boundary of the lower aluminum mining face (5) as the construction area (6) of the target rock stratum; S22. Arrange the wellhead on the left side of the construction area (6), use a single-bend screw drill to vertically drill a first vertical main well (7) directly to the target rock stratum on the ground, and synchronously carry out the operations of installing the casing and cementing the pipe; S23. Continue to drill horizontally to the right to the first horizontal main well (8) at the right boundary of the construction area (6), and synchronously carry out the operations of installing the casing and cementing the pipe; S24. Adopt the method of backward side drilling to drill horizontal branch wells (9) on both sides of the first horizontal main well (8); the horizontal branch wells (9) located on both sides of the first horizontal main well (8) are distributed in a plume shape; S25. Install a tubing (10) in the first vertical main well (7) and the first horizontal main well (8), pump the coal gangue-based slurry into the horizontal branch well (9) through the tubing (10), and inject the coal gangue-based slurry into the target rock stratum through a grouting pipe (11); S26. Adopt the backward method to carry out the grouting operation of the next horizontal branch well (9) until the construction of the entire construction area (6) is completed; S3. In-situ pre-fracture of bauxite: Adopt the horizontal directional drilling grouting technology to inject fracturing fluid into the aluminum layer (300) to cause fractures in the bauxite in the aluminum layer (300); The step S3 includes the following sub-steps: S31. Use a single-bend screw drill to extend into the first vertical main well (7) and vertically drill a second vertical main well (12) directly to the aluminum layer (300) at the turning point of the first vertical main well (7), and synchronously carry out the operations of installing the casing and cementing the pipe; S32. Continue to drill horizontally to the right to the second horizontal main well (13) at the right boundary of the aluminum mining face (5), and synchronously carry out the operations of installing the casing and cementing the pipe; S32. Install a fracturing pipe (14) in the second vertical main well (12) and the second horizontal main well (13), and install a fracturing device (15) at the front end of the fracturing pipe (14); S33. Pump the fracturing fluid into the fracturing device (15), and the fracturing device (15) injects the fracturing fluid into the aluminum layer (300) to cause fractures in the bauxite in the aluminum layer (300); S34. Adopt the backward method to complete the fracturing of the bauxite in the entire aluminum mining face (5); S4. Pillarless fully mechanized bag filling mining: Divide the aluminum layer (300) into several ore blocks (1) of preset length along the mining direction; as the fully-mechanized mining equipment (2) advances forward, hang filling bags (3) on the roof of each mined ore block (1) in sequence, and pump red mud-based slurry (4) into the filling bags (3) to support the ore block (1) after solidification; the red mud-based slurry (4) is a mixture of red mud fine aggregate, cement and water; the composition mass ratio of the red mud-based slurry (4) is red mud fine aggregate:cement:water = 1:0.2:0.7, so that the compressive strength of the solidified filling body can reach 20 MPa.

2. The green mining method for bauxite under coal according to claim 1, wherein The fracturing fluid is a mixture of water, sand and additives.

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